Centrifuge apparatus adapted to separate liquid samples based on density generally contain a plurality of containers mounted on the ends of a series of outwardly extending rotor arms and into which are located detachably mounted sample inserts. Best operation of the centrifuge occurs when the system is perfectly balanced with each of sample containers containing an identical amount of sample liquid. In practice, however, the load on a centrifuge rotor is seldom balanced. In a typical procedure, the number of samples processed may be less than the number of centrifuge components available. Also, the amounts of fluid sample among the various sample compartments are generally different. Under an imbalanced condition, as the rotor is spun, vibrations are generated that tend to damage the motor bearing and may lead to beqring failure. Also, vibrations reduce the safe operable speed of the rotor and tend to agitate any interface formed between constituents of a sample being separated. In an extreme case, failure of the motor bearing may cause destruction of the centrifuge during a "run".
Several self-balancing systems have been developed in order to cause the centrifuge to become balanced during a run in order to avoid the problems described above. These systems, such as the one disclosed in Finkel U.S. Pat. No. 3,921,898, typically provide a mass distribution means, such as fluid or solid weights, that are automatically distributed among the sample containers to equalize or balance the centrifuge rotor about its vertical motor drive shaft. Mass redistribution systems provided in automatic balancing systems for centrifuges, of which I am aware, cause the balancing fluid or solid weights to be distributed about the center of rotation of the rotor during a run, not before. Although balancing is completed within a relatively short period of time, the rotor does spin in an unbalanced condition until steady state rotation is reached. In circumstances when only a minor initial imbalance exists, there is no substantial deleterious effect caused to the sample or centrifuge. In circumstances where there is a significant initial imbalance, on the other hand, significant stresses on the motor bearing from start up to steady state are created, reducing the life time of the bearing and interfering with stratification of the samples. In extreme cases, the entire centrifuge has been known to become unstable, resulting in an explosion of the centrifuge mechanism. A need exists, therefore, for a self balancing centrifuge, wherein balancing is automatically completed in a static mode, that is, prior to a centrifuge run.
One object of the present invention, therefore, is to provide a new and improved centrifuge, wherein automatic, static balancing is made.
Another object is to provide a new and improved, self-balancing centrifuge of a type having balancing fluid storage tanks carried by the sample containers, wherein distribution of fluid among the tanks for balancing is made prior to rotation of the centrifuge rotor.
Another object is to provide a new and improved method of balancing a centrifuge, wherein the total mass carried by the rotor is re-distributed for balancing prior to rotation of the centrifuge rotor to eliminate the possibility of centrifuging in an unbalanced condition.